According to the present invention there is provided an aerodynamic device having a rotor coupled to retaining means which define an axis of rotation for the rotor, the rotor comprising a wall which extends between two spaced positions on the axis and is spaced from the axis between said positions, the axis of rotation of the rotor passing through or adjacent to its centre of gravity.
When there is relative movement between the air and the rotor the rotor rotates and in so doing it modifies the air flow in the region of the rotor so that it experiences an aerodynamic lift force. The lift force is accomplished by a relatively small drag force.